The goal of this project is to identify mechanisms mediating effects of endogenous TGF-b1 on the development, function, and malignant transformation of hematopoietic cells, with a primary emphasis on lymphoid lineages. Experimental evidence from in vitro studies of function suggest a critical role for TGF-b1 in regulating myelopoiesis and immune cell function, but such studies are limited by their inability to reproduce the complex in vivo network which ordinarily influences the genesis and function of these cell populations. Our approach to this problem has been to utilize the TGF-b1-null mouse, as well as complimentary vivo model systems characterized by a disruption in genes encoding components of the TGF-b signaling pathway. This approach has enabled us to identify critical links between cell cycle control by TGF-b1, immune cell maturation and function, and hematopoietic cell growth and differentiation, as they occur in vivo. Examples include our demonstration of myeloid hyperplasia as a distinct phenotype in TGF-b1-null mice, and of novel autocrine effects of TGF-b1 in the autoimmune and hematopoietic manifestations of TGF-b1 deficiency. Our collaborative efforts have led to important discoveries regarding the: epidermal dendritic cell (DC) requirement for TGF-b1 (Mark Udey, NCI) and DC antigen trafficking (Shin-Ichi Hayashi, Tottori University); role of the TGF-b1-intermediate Smad3 in mucosal immunity, T cell function, chemotaxis, MCH class II and class II transactivator expression, and in suppression of IL-2 expression (Chuxia Deng, NIH;Tika Benvinista, UAB); role of TGF-b in plasmacytomagenesis (Mike Potter, NCI); TGF-b-independent effects of CTLA4 (Jim Allison, U.C. Berkeley); haploinsufficient tumor suppressor function of TGF-b1 (Lalage Wakefield, NCI and Andy Koff, Memorial Sloan Kettering); and a role of p21cip1 in activated immune cells and of TGF-b in intestinal tumorigenesis (Chuxia Deng, NIH). To define the molecular events through which TGF-b governs hematopoietic stem cell differentiation and commitment, we are developing new approaches that include conditional and lineage-specific disruption of TGF-b ligand and signaling intermediates. We have also developed a system for creating hematopoietic stem cell lines from a single yolk sac of mice carrying mutations in critical, pathway restricted Smad signaling intermediates. These lines will be invaluable in assessing the TGF-b/bone morphogenetic protein (BMP)-specific effects on hematopoietic development and reconstitution. Studies such as immune reconstitution in chimeric mouse models and in vitro assays of differentiation are currently underway and promise to provide mechanistic insights into how this family of proteins controls blood cell development and function. Finally, we maintain an emphasis on translational research, aiming to move our observations toward development of useful clinical tools and potential therapies. As part of this effort, our laboratory is the first to successfully develop functionalized, biologically active epitope-tagged TGF-b proteins and to design diagnostic and potential therapeutic approaches based on the application of such proteins. More importantly, these reagents will prove invaluable in developing new transgenic models in which epitope-tagged TGF-b isoforms can be expressed in a spatially and/or temporally restricted manner. Future studies employing systemic administration of TGF-b either in disease models or in the clinic will benefit from the availability of a readily detectable epitope-tagged-TGF-b.